Neck tension ?

[madmixerman]

If brass is resized using a .265 bushing and another piece was resized with a .264 bushing and then both were run through an expander die, will the neck tension be the same after they were run through the expander ?
Edit: Forgot to say brass is annealed before resizing.

 

[Bill Norris]

Should both be the same after running thru the expander.

 

[JFrank]

What if one piece had a thousandths more spring back than another ?

 

[mjl650]

Check them with pin gauges.

 

[Straightshooter1]

If brass is resized using a .265 bushing and another piece was resized with a .264 bushing and then both were run through an expander die, will the neck tension be the same being that it was run through the expander ?
Edit: Forgot to say brass is annealed before resizing.

Given all other things being equal (or very little difference) between them, e.g. neck thickness, consistent annealing, etc. . . . neck tension should be the same.

 

[RegionRat]

When we push a ductile metal around, there is a part of the strain that is within the elastic region, and if taken too far goes into the plastic, or yield, region.

When a cartridge neck is sized, forcing the neck into tooling would be called a forced strain. When left on the tooling for longer, the result can vary a little with a more complicated phenomenon burried within that elastic modulus. The modulus of cartridge brass has a shear storage and shear loss component that means sometimes the answer depends on the speed or time on the tooling.

When all is said and done, once you move a neck far enough (strain) you go past the yield point (stress) and that amount is affected by the speed and work hardened condition of the brass history. Your example was annealed, so let’s assume it was low to medium work hardened.

The neck thickness and the chamber dimension would determine how different the two bushings would end up, but both are capable of getting the stress into the yield zone where the neck tension would be slightly different between those two bushings.

To see if the expander actually moves the neck tension, some testing is required. If the expander diameter doesn’t push the neck far enough as when it is within the elastic region, then you have to step up the pin diameter to see any change.

These concepts are easier to show with diagrams, but those take lots of time to produce and I’m only catching small breaks, sorry.

 

[mikecr]

When you seat bullets in the necks they will be at cal ID.
Pull bullets and notice they spring back to smaller but same ID.
Still, tension (bullet grip) is the force of that spring back (not the distance), against some area of bullet bearing.
Currently none of us have a means to measure this force, but you haven't described anything that would change it. IMO, they'll shoot the same.

 

[D-4297]

As Mr. Spock would say : Logic dictates ; that because a variation has been introduced into the equation , ( Two different bushings ) then the variation would , in-fact , be present in the cases . No matter how minute , or even measurable . But would have minimal effect towards the end result . Shoot-em , Homer .

 

[Tod Hendricks]

If brass is resized using a .265 bushing and another piece was resized with a .264 bushing and then both were run through an expander die, will the neck tension be the same being that it was run through the expander ?
Edit: Forgot to say brass is annealed before resizing.

No. Well it depends on how you define tension. It will take more pressure to seat bullets in brass with a smaller neck ID prior to expanding with the same size mandrel.

 

[Ned Ludd]

The answer to your question also depends on the diameter of the expander mandrel in relation to the [inside] neck diameter. It would be possible to select a mandrel that might barely open up one neck and not touch the other. If the mandrel was solidly opening up both of the necks (i.e. doing work on both), the final neck tension should be close, in theory. In practice, I've observed some funny things happen with expander mandrels when the bushing initially selected to size the necks down left the neck diameter very close to the same diameter as the later mandrel step would leave them. I always try to use a bushing at least .001" under the diameter the mandrel is expected to produce, so that the mandrel is actually doing work to expand every single neck.

Using an expander mandrel on necks sized with bushings having a .001" variance is probably not a great idea, even if you get away with it this time. You can probably tell from measurements if there is a big difference afterward, which would likely be due to a difference between the spring-back of the two necks after sizing with the different bushings. However, the easiest fix is simply to size all the necks with the same bushing, i.e. re-sizing some cases with the appropriate bushing, if necessary.

 

[243winxb]

No

 

[mikecr]

The final expansion mandrel is the bullet.